JPH0737954B2 - Organic solvent vapor detection method - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a method for detecting high-concentration organic solvent vapor, and in particular, it suppresses the deterioration of a gas sensor while suppressing the organic solvent vapor generated during semiconductor cleaning in a semiconductor manufacturing plant. Regarding the method of detecting.

[Prior Art] The inventors have examined the detection of organic solvent vapor generated by cleaning a silicon substrate in a semiconductor manufacturing factory.
The solvent used is mainly isopropanol or acetone, and the cleaning is performed by, for example, immersing a silicon substrate of a work-in-progress in the solvent. The concentration of the generated organic solvent vapor was about 2000 ppm in the duct above the cleaning tank. Further, when the in-process product was pulled up from the cleaning tank, a peak of the solvent vapor concentration occurred, and the concentration was about 5000 ppm.

The problem that occurred here was that the gas sensor deteriorates due to contact with high-concentration organic solvent vapor. SnO2 and Fe2O3
In the case of metal oxide semiconductor gas sensors such as those mentioned above, a decrease in sensor resistance usually occurred. Further, in the case of the catalytic combustion type gas sensor, the output decreased due to the decrease in catalyst activity. Further, since the gas concentration is high even under normal conditions, the tolerance of the detected concentration is small, which complicates the problem.

Here, the related prior art will be described as follows.
Japanese Patent No. 6,860 proposes that alcohol vapor in the fermentation liquor be sampled by a gas permeable membrane such as a Teflon membrane and detected by a metal oxide semiconductor gas sensor. This publication also states that the same technique can be used for sampling CO, methane, hydrogen, etc. from a flue.

Next, JP-A-59-104,583 discloses diluting highly concentrated radioactive gas in a nuclear power plant or the like to about 1/1000 to 1 / 100,000 and sampling. The purpose of detection here is radiation measurement, not detection of combustible gas by a gas sensor. The purpose of dilution is also to weaken the radiation from the sample and reduce the risk of exposure.

Further, Japanese Patent Publication No. 53-31794 discloses that a gas permeable film such as a Teflon film is used to detect gas such as sulfur dioxide in a flue gas.
It indicates that the sample is diluted to 1/1000 to 1 / 100,000. The analyzer used is a detector such as a flame photometric detector.

However, none of the prior arts has examined the detection of high-concentration organic solvent vapor generated during semiconductor cleaning.

[Problem of the Invention] An object of the present invention is to suppress deterioration of a gas sensor due to contact with a high-concentration organic solvent vapor without using a diluent gas, and to accurately detect an organic solvent vapor during semiconductor cleaning. .

[Structure of the Invention] The present invention provides a method for detecting an organic solvent vapor generated by cleaning a semiconductor in a semiconductor manufacturing plant with a metal oxide semiconductor gas sensor or a catalytic combustion gas sensor, for exhausting the organic solvent vapor. The duct is provided with a branch pipe, the gas sensor is installed in the branch pipe, and the concentration of the organic solvent vapor in the branch pipe is reduced at a predetermined ratio without using a diluent gas due to the oxidation activity of the gas sensor. It is characterized by detecting.

The cause of the deterioration of the gas sensor is contact with high-concentration organic solvent vapor, and deterioration can be suppressed by lowering the solvent vapor concentration. The metal oxide semiconductor gas sensor and the catalytic combustion type gas sensor have oxidative activity, and if the oxidative activity oxidizes the organic solvent vapor in the branch pipe, the concentration of the organic solvent vapor can be reduced without a diluent gas. Then, the detection accuracy is slightly reduced due to this.

That is, in the case of a metal oxide semiconductor gas sensor, the logarithm of the resistance value of the sensor changes linearly with the logarithm of the gas concentration.
Even if the gas is diluted here, the ratio of the resistance values at the two gas concentrations is almost constant. What is important in detection is not the ratio of the resistance values in clean air and the organic solvent vapor, but the dependence of the sensor resistance on the organic solvent concentration.
The gas concentration dependency does not change even when the steam is diluted. Next, consider the case where gas is detected from the heat of combustion in the catalytic oxidation catalyst. The output in this case is proportional to the gas concentration. If the gas concentration is decreased here, the output also decreases.
But the problem is not the size of the output, but its reliability.
Then, it is easy to amplify the output, and the small output itself does not pose a problem. Of course, comparing the metal oxide semiconductor gas sensor and the catalytic combustion type gas sensor,
The metal oxide semiconductor gas sensor is superior because the catalytic combustion gas sensor is accompanied by a decrease in output.

The gas sensor used is a metal oxide semiconductor gas sensor utilizing a change in the resistance value of the metal oxide semiconductor, or a catalytic combustion gas sensor that detects the heat of combustion in the catalytic oxidation catalyst with a resistance temperature detector. The solvent vapor concentration is 1/2 to 1/100.
It is preferable to reduce it to a certain degree. The ratio of decrease in density is determined by the balance between prevention of sensor deterioration and background noise, and more preferably 1/4 to 1/40.

[Example] FIG. 1 shows an example of detection of isopropanol at the time of cleaning a silicon substrate in a semiconductor manufacturing factory. In the figure, (02) is a pure water tank, (04) is an isopropanol tank, and after cleaning the silicon substrate of the in-process product with pure water,
Wash with isopropanol. Work in progress moves as shown by the black arrows in the figure. A duct (06) is provided above the isopropanol tank (04) to suck the isopropanol into a solvent recovery device (not shown). Such a device is placed in a clean room, and fluctuations in temperature and humidity inside the room are small.

(2) is a gas sensor utilizing a change in resistance value of a metal oxide semiconductor such as SnO2, Fe2O3, or In2O3, and a gas sensor "TGS109" manufactured by Figaro Giken Co., Ltd. was used for the experiment. The characteristics of this sensor are well known. A branch pipe (3) is connected to the duct (06), a sensor (2) is arranged in a detection chamber (4) at the tip of the duct (06), and a Teflon membrane (6) as a ventilation resistance is arranged in the branch pipe (3). . The Teflon membrane (6) can be replaced by any ventilation resistance, the position of which is in the branch tube (3),
Any position may be used as long as it can delay the diffusion of the atmospheric gas into the sensor (2). For example, the cover (not shown) of the sensor (2) may be covered with the Teflon film (6). A constant flow pump or the like may be connected to the detection chamber (4) to introduce the atmosphere into the detection chamber (4) at a constant flow rate.

(8) is the load resistance connected to the sensor (2) and is the power supply + Vcc
(10) is a comparison circuit, and (12) is an alarm means such as a buzzer or an LED. (14) is a power circuit for raising the sensor output, for example, the voltage applied to the load resistance (8), to obtain an output proportional to the gas concentration, and (16) is a recorder. Of course, the sensor (2) may be replaced by a catalytic combustion type sensor or the like, and in this case, a well-known accessory circuit can be used.

The operation of this device will be described. Place the silicon substrate in the pure water tank (0
Wash in 2), then soak in isopropanol bath (04), pull up and dry. Each step is repeated in a cycle of about 10 minutes. Vapor from the isopropanol tank (04) is sucked through the duct (06). The isopropanol concentration in the duct (06) is about 2000 ppm on average, and when the silicon substrate is pulled up, a peak with a width of about 1 minute occurs at a concentration of about 5000 ppm.

The organic solvent from the duct (06) diffuses into the detection chamber (4) through the Teflon film (6). Teflon film here (6)
Due to the ventilation resistance of the sensor and the oxidation activity of the sensor (2), the solvent concentration in the detection chamber (4) decreases at a predetermined ratio. The ratio of decrease in concentration is determined by the diffusion rate of vapor by the Teflon film (6) and the oxidizing activity of the sensor (2), and the preferable range is 1/2.
1/100, more preferably 1/4 to 1/40, and here 1/10. How much the concentration is reduced depends on prevention of deterioration of the sensor (2) and the magnitude of background noise. In the case of both the metal oxide semiconductor gas sensor (2) and the catalytic combustion type gas sensor, the sufficiently preferable condition is that the average gas concentration under normal conditions is less than 1/40 of the explosion lower limit concentration (LEL) It is to make the gas concentration 1/200 or more of LEL. The conditions of 1/4 to 1/40 mentioned above correspond to this.
This is because in the case of organic solvent vapor, the combustion heat at the lower explosion limit concentration is almost constant regardless of the type of solvent, and the influence on the sensor (2) is also determined by the ratio of the concentration to the lower explosion limit concentration. In the case of the embodiment, since the apparatus is placed in a clean room and the temperature and humidity fluctuations are small, the day difference fluctuation of the sensor is slight and the background noise does not pose a problem even when the gas concentration is reduced to 1/100.

The gas sensor (2) detects the organic solvent having the lowered concentration, and outputs the detection signal as a change in the voltage of the load resistance (8). Next, if the gas concentration is, for example, 8000 ppm (value converted to the concentration of the duct (06)), the comparison circuit (10)
To activate the alarm. The recorder (16) records changes in gas concentration. In the case of the catalytic combustion type gas sensor, for example, a compensating piece is connected to the sensor and incorporated in a bridge circuit, and the output of the bridge circuit is used as a detection signal.

The characteristics of the apparatus of FIG. 1 are shown in FIG. The horizontal axis is isopropanol concentration, the lower explosion limit is 20,000 ppm, and the alarm concentration is 8
000ppm The vertical axis represents the resistance value of the sensor (2), and the sensor temperature is 400 ° C. The solid line 51 shows the characteristics when the gas is not diluted, and the solid line 52 shows the characteristics when the concentration is reduced to 1/10. The resistance value of the sensor (2) is inversely proportional to the 0.8th power of the gas concentration. When the sensor (2) was placed in the duct (06) and used for 120 days, the characteristic changed to a broken line. On the other hand, in the example, it changed like a chain line.

FIG. 3 shows the results when using a catalytic combustion type gas sensor. The sensor was an alumina carrier carrying a Pt80% -Rh20% catalyst, and was used at 400 ° C for 120 days. The solid line 61 shows the characteristics when the gas is not diluted, and the solid line 62 shows the characteristics when the gas is diluted to 1/10. The vertical axis is the output of the bridge circuit incorporating the sensor. The output is proportional to the gas concentration, and if the concentration is reduced to 1/10, the output will also be 1/10. However, the degree of deterioration is significantly reduced.

FIG. 4 shows the characteristics over time when the metal oxide semiconductor sensor (2) was used. The result is an average of 4 sensors, 5000pp
The load resistance was set to alert with m isopropanol. Energize in clean air for the first 30 days, then 120
It was used for the detection of isopropanol daily, and the change in alarm concentration was investigated. The solid line shows the results in the example of FIG. 1 (dilution rate 1/10)
Shows the result of setting in the duct (06) with a broken line.
In the comparative example, the alarm point drops to 2000 ppm in 120 days,
In the example, it is almost stable.

Table 1 shows the changes over time for 120 days when the catalytic combustion gas sensor was used. The measuring method is the same as in FIG. 4, and the sensor is the one described with reference to FIG.

Although a specific embodiment has been described here, the invention is not limited to this. The same applies even if the isopropanol is replaced with another solvent such as ethanol, acetone, or benzene.

[Advantages of the Invention] According to the present invention, a high-concentration organic solvent generated at the time of cleaning a semiconductor can be accurately detected without using a diluent gas while suppressing deterioration of the gas sensor.

[Brief description of drawings]

FIG. 1 is a diagram showing the arrangement of the embodiment, and FIGS. 2 to 4 are characteristic diagrams of the embodiment. In the figure, (04) …… isopropanol tank, (06) …… duct,
(2) ... Gas sensor, (3) ... Esuga (3), (6) ... Teflon membrane.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Susumu Yasunaga 1-5-3 Senba Nishi, Minoh City, Osaka Prefecture Figaro Giken Co., Ltd. (72) Hideo Matsuzaki 1-4-5 Nishi-Shimbashi, Minato-ku, Tokyo No. Tokuyama Soda Co., Ltd. Tokyo Branch (56) References JP-A-57-17848 (JP, A) JP-A-58-158551 (JP, A) Actual development 61-206860 (JP, U)

Claims (2)

[Claims] 1. A method for detecting an organic solvent vapor generated by cleaning a semiconductor in a semiconductor manufacturing plant by a metal oxide semiconductor gas sensor or a catalytic combustion type gas sensor, wherein a duct for exhausting the organic solvent vapor is branched. The gas sensor is installed in the branch pipe, and the concentration of the organic solvent vapor in the pipe is reduced at a predetermined ratio without using a diluent gas due to the oxidation activity of the gas sensor, and the vapor is detected by the gas sensor. A method for detecting an organic solvent vapor, comprising: 2. The method according to claim 1, wherein the concentration of the organic solvent vapor is reduced to 1/2 to 1/100.